Generally, in an image-forming apparatus for forming images by using the electrostatic photographic method, an electrostatic latent image, which is formed on the surface of an image-bearing device such as a photoconductor drum, is developed by developer (hereinafter, referred to as toner), and this toner image is transferred onto a copy material such as a sheet of copy paper, thereby producing a copied image. In this system, in order to obtain copied images with good quality, it is essential to remove residual toner as well as foreign matters from the surface of the image-bearing device sufficiently. These foreign matters include paper particles, talc and kaolin derived from sheets of copy paper. For this reason, in order to remove residual toner as well as these foreign matters, there have been proposed various cleaning devices which are provided with a fur brush, a cleaning blade, a cleaning web, and other members, and which allow these cleaning blade and other members to come into contact with the surface of the image-bearing device.
However, these cleaning devices only have an arrangement wherein residual toner is scraped off from the surface of the image-bearing device by pressing the cleaning blade and other members onto the surface of the image-bearing device. In this arrangement, the cleaning device tends to cause scratches on the surface of the image-bearing device. Therefore, the cleaning device tends to shorten the life of the image-bearing device and cause adverse effects on the picture quality of copied images. Further, although the cleaning device is inexpensive, it fails to sufficiently remove the above-mentioned foreign matters that are likely to scatter. Moreover, it is necessary to install a waste-toner collecting container for storing residual toner removed by the cleaning device; this make it difficult to achieve a compact image-forming apparatus.
In order to solve the above-mentioned problems, various proposals have been made. For example, Japanese Laid-Open Patent Publication No. 100585/1980 (Tokukaishou 55-100585) discloses a cleaning device which is provided with a sponge-like porous elastic member.
Moreover, for example, Japanese Laid-Open Patent Publication No. 107678/1985 (Tokukaishou 60-107678) discloses a cleaning device which is provided with an insulating member. This cleaning device has an arrangement wherein the surface electric potential of the insulating member is set to be higher than the surface electric potential of the image-bearing device so that residual toner is removed by the use of electrostatic force. More specifically, as shown in FIG. 14, the image-bearing device (not shown) has its surface charged to a predetermined negative electric potential V.sub.SP' by a main charger, and is allowed to have an electrostatic latent image on its surface. Next, this electrostatic latent image is developed by toner that has been positively charged, and is transferred onto a copy material. Then, after the transferring process, the residual toner is kept at a positively charged state. Here, a negative electric potential V.sub.CL', which has an absolute value greater than that of the charged electric potential V.sub.SP' of the image-bearing device, is applied to the insulating member. Consequently, the residual toner, which has been positively charged, is affected by an electric field e' that has been formed by the image-bearing device and the insulating member, and is separated from the surface of the image-bearing device to adhere to the insulating member. Thus, the insulating member, that is, the cleaning device, removes the residual toner.
Moreover, for example, Japanese Laid-Open Patent Publication No. 142373/1983 (Tokukaishou 58-142373) and Japanese Laid-Open Patent Publication No. 261379/1988 (Tokukaishou 63-261379) disclose cleaning devices each of which is provided with a cleaning member and a contacting member that comes into contact with the cleaning member. These cleaning devices have an arrangement wherein the cleaning member is charged to have a electric potential whose polarity is reversed to that of the toner electric potential by friction between the cleaning member and the contacting member and an electrostatic force thus exerted is used for removing the residual toner and the foreign matters.
However, in the cleaning device disclosed by Japanese Laid-Open Patent Publication No. 100585/1980 (Tokukaishou 55-100585), the sponge-like porous elastic member is pressed onto the surface of the image-bearing device so that the residual toner is scraped off from the surface of the image-bearing device. For this reason, it is impossible to avoid the above-mentioned problems.
Further, in the cleaning device disclosed by Japanese Laid-Open Patent Publication No. 107678/1985 (Tokukaishou 60-107678), the following problems are raised when it is used in an image-forming apparatus wherein the positive developing method is adopted. For example, when amorphous selenium or other materials is used to constitute the image-bearing device, the image-bearing device is positively charged, while the toner is negatively charged, so as to form a toner image. For this reason, when the surface electric potential of the insulating member is made to become higher than the surface electric potential of the image-bearing device, the residual toner tends to adhere to the insulating member. Therefore, in order to store the residual toner removed by the insulating member into the waste-toner collecting container, a cleaning member for scraping the residual toner off from the insulating member has to be installed in a separated manner. Moreover, in the cleaning device, a cleaning blade is used together with the insulating member combinedly. Consequently the cleaning device fails to overcome the above-mentioned problems.
Furthermore, in the cleaning devices disclosed by Japanese Laid-Open Patent Publication No. 142373/1983 (Tokukaishou 58-142373) and Japanese Laid-Open Patent Publication No. 261379/1988 (Tokukaishou 63-261379), although it does not cause scratches on the surface of the image-bearing device, it requires a waste-toner collecting container; this makes it impossible to achieve a compact image-forming apparatus.